1. Field of the Invention
The present invention relates to a projection-type liquid-crystal display device such as a light source device used in a projector, and particularly to a compact light source device suitable for use in a compact projector.
2. Description of the Related Art
In conventional practice, projectors in which images on liquid-crystal display elements are magnified, projected, and displayed are configured such that a single liquid-crystal display element is illuminated by a metal halide lamp from behind, and the image displayed by the liquid-crystal display element is magnified and projected by a projection lens.
For example, Japanese Unexamined Patent Applications (Kokai) 62-237485, 3-75737, and 8-111107 describe inventive structures in which a metal halide lamp or a halogen lamp are used as the light source, and light emitted by this light source is transmitted through a hollow light-guide structure and directed toward a liquid-crystal display element.
The above-described prior art, however, involves using a lamp as the light source, and is limited in the degree to which the size of the light source as such can be reduced. It is thus difficult to reduce the size of the projector as a whole. Portable communication terminal devices have appeared in recent years, dispensing with the need to project images to dimensions in excess of 60 inches with such projectors. It is proposed, for example, that the size of a projected image be reduced to about 10 or 20 inches. At this size of a projected image, a light-emitting element (light-emitting diode, semiconductor laser, etc.) or the like can be used as the light source, making it possible to design very small projectors.
Light-emitting elements and other miniature light-emitting devices are substantially point light sources, and it is therefore difficult to uniformly illuminate a liquid-crystal display element having a given surface area. An attempt to line up a plurality of light-emitting diodes and to illuminate a wide surface area ultimately yields an assembly of point light sources, resulting in a nonuniform distribution of light intensity in a two-dimensional plane.
Japanese Unexamined Patent Application 10-123512 discloses projector technology in which the light source is made up of a two-dimensional array of light-emitting diodes. Light from the light-emitting diodes is converted to planar light by microlens array (an array of lens elements formed in conformity with the light-emitting diodes) in order to allow light radiated by the light-emitting diodes (point light sources) to be directed toward light-crystal display elements in an efficient manner.
Such microlens arrays are disadvantageous, however, in that the lens action along the border between adjacent lens elements becomes weak as a result of manufacturing errors or the like, making it difficult to create uniform illumination light.
According to another arrangement, which is disclosed in Japanese Unexamined Patent Application 9-73807, the optical axis can be cured 90° to guide the light, but a technique has yet to be found that would allow the optical axis of a point light source top advance in a straight line, yielding planar light.